It has heretofore been known that titanium based catalysts composed of a titanium compound and an organoaluminum compound are used as catalysts for the preparation of .alpha.-olefin polymers, for example, ethylene polymers or ethylene/.alpha.-olefin copolymers.
Generally, olefin polymers obtained with the titanium based catalysts have a broad molecular weight distribution and a broad composition distribution in particular and are poor in surface non-tackiness and transparency.
On the one hand, there have been proposed recently processes for the preparation of ethylene/.alpha.-olefin copolymers using catalysts composed of zirconium compounds and aluminoxanes as new type of Ziegler catalysts for olefin polymerization.
Olefin polymers obtained with the above-mentioned new type of Ziegler catalysts for olefin polymerization usually have a narrow molecular weight distribution and a narrow composition distribution. On this account, olefin polymers which have a broad molecular weight distribution according to the purposes for which they are used and which are excellent in moldability have ardently been desired.
Further, it is difficult to obtain olefin polymers having a high molecular weight by polymerization or copolymerization of olefins in the presence of transition metal compound catalysts containing ligands having a cycloalkadienyl skeleton. Accordingly, it has been desired that transition metal compound catalysts containing ligands having a cycloalkadienyl skeleton which are capable of giving olefin polymers having a high molecular weight be developed to make their appearance.